4.146
SEL-751 Relay Instruction Manual Date Code 20170927
Protection and Logic Functions
Group Settings (SET Command)
reclosing never takes place (reclosing is never initiated). The reclosing relay is
effectively inoperative.
If the following setting is made:
79RIS := 0 (numeral 0)
reclosing never takes place (the reclosing relay goes directly to the lockout
state any time reclosing is initiated). The reclosing relay is effectively inopera-
tive.
Drive-to-Lockout and Drive-to-Last Shot Settings (79DTL and 79DLS,
Respectively)
When 79DTL := logical 1, the reclosing relay goes to the lockout state (Relay
Word bit 79LO = logical 1), and the front-panel LO (Lockout) LED illumi-
nates.
79DTL has a 1 second dropout time. This keeps the drive-to-lockout condition
up 1 second after 79DTL has reverted back to 79DTL := logical 0. This is use-
ful for situations where both of the following conditions are true:
➤ Any of the trip and drive-to-lockout conditions are “pulsed”
conditions (e.g., the OPEN command Relay Word bit, OC,
asserts for only 1/4 cycle—refer to Factory Settings Example
on page 4.146).
➤ Reclose initiation is by the breaker contact opening (e.g., 79RI
:= NOT 52A—refer to Additional Settings Example on
page 4.145).
Then the drive-to-lockout condition overlaps reclose initiation and the
SEL-751 stays in lockout after the breaker trips open.
When 79DLS := logical 1, the reclosing relay goes to the last shot, if the shot
counter is not at a shot value greater than or equal to the calculated last shot
(see Reclosing Relay Shot Counter on page 4.144).
EXAMPLE 4.21 Factory Settings Example
The drive-to-lockout factory setting is:
79DTL := OC OR SV04T
Relay Word bit OC asserts for execution of the OPEN command. See the Note
in the lockout state discussion, following Table 4.53.
Relay Word bit SV04T asserts for execution of the OPEN command from the
front-panel pushbutton (see Table 8.4 for more detail).
The drive-to-last shot factory setting is:
79DLS := 79LO
One open interval is also set in the factory settings, resulting in last shot = 1.
Any time the relay is in the lockout state (Relay Word bit 79LO = logical 1),
the relay is driven to last shot (if the shot counter is not already at a shot
value greater than or equal to shot = 1):
79DLS := 79LO = logical 1
Thus, the relay is driven to the lockout state (by setting 79DTL) and,
subsequently, last shot (by setting 79DLS).
EXAMPLE 4.22 Additional Settings Example
To drive the relay to the lockout state for fault current greater than a
certain level when tripping (e.g., level of phase instantaneous
overcurrent element 50P3P), make settings similar to the following:
79DTL := TRIP AND 50P3P OR
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